Multistage hydraulic cylinder



'PMT

March 5, 1957 F. H. TENNIS 2,783,744

MULTISTAGE HYDRULICV CYLINDER Filed sept. 21, 1955 2 sheets-shet 1 March 5, 1957 F. H. TENNIS MULTISTAGE HYDRAULIC CYLINDER 2 Sheets-Sheet 2 Filed Sept. 21, 1955 United States Patent O M' MULTISTAGE HYDRAULIC CYLlNDER Francis H. Tennis, Milwaukee, Wis., assignor to Hydraulic Unit Specialties Co., Pewaukee, Wis., a corporation of Wisconsin Application September 21, 1955, Serial No. 535,569

7 Claims. (Cl. 121-46) This invention relates to iluid pressure operated devices and has more particular reference to hydraulic cylinders of the telescoping or multistage type.

Generally speaking, telescoping hydraulic cylinders of this type are especially useful wherever the load or mechanism to be operated must be moved a substantially great distance and where space limitations preclude the use of the more conventional single stage cylinder. The retracted length of a single stage cylinder is approximately equal to the length of its working stroke While the retracted length of a three stage telescoping cylinder having the same working stroke, for instance, need not be more than one-half the length of its stroke.

While the compactness of the telescoping or multistage cylinder makes it ideal for use wherever space is at a premium, their design characteristics are such that it is quite difficult to adapt them for use other than as single acting or lifting cylinders. 1n such single acting cylinders, the load or mechanism operated by the cylinder is relied upon to eect retraction of the Various stages thereof, and thus limits their usefulness to applications where the load always resists extension of the cylinder. Without resorting to quite complicated and costly constructions, multistage hydraulic cylinders cannot be ernployed in cases where the mechanism operated by the cylinder exerts a force tending to effect extension of the cylinder, for example, during extension of the linal stage cylinder or at some point shortly before the full working TL stroke of the unit is reached.

It is a purpose of this invention, therefore, to provide a telescoping or multistage hydraulic cylinder of the character described which features exceptional utility through the incorporation therein of simple and inexpensive but "7 reliable means for achieving double acting operation of its nal stage cylinder.

More specifically, it is a purpose of this inventionfto provide a multistage hydraulic cylinder comprising a number of single acting cylinders and a double acting final stage cylinder, and featuring a hollow piston rod for the nal stage cylinder along with a simple check valve mechanism in the piston thereof by which the unit is automatically converted from double acting operation of 11 its final stage cylinder at the start of retraction to single action operation after the piston rod of the finalV stage cylinder has been fully retracted.

With the above and other objects in view, which will appear as the description proceeds, this invention resides structed according to the best mode so far devised for 2,783,744 Patented Mar. 5, 1957 ICC 2 the practical application of the principles thereof, and in which Figure 1 is an elevational view of a multistage hydraulic cylinder embodying the principles of this invention, showing the same fully retracted but with parts thereof broken away and shown in section;

Figure 2 is a fragmentary View thereof showing the plunger of the nal stage cylinder fully extended; and

Figure 3 is a fragmentary view thereof showing the piston of the final stage cylinder close to its retracted position.

Referring now more particularly to the accompanying drawings in which like numerals indicate like parts throughout the several views, the numeral 5 generally designates a three stage hydraulic cylinder which, in Figure l, is shown in its fully retracted position. The unit comprises an'outer or first stage cylinder 6 encircling a second stage cylinder 7, and a third stage cylinder 8 inside the second stage cylinder. These cylinders are all of about the same length, and while the outer cylinder 6 may be considered stationary, the second and third` stage cylinders are axially movable relative to one another and to the outer cylinder.

As is customary in multistage hydraulic cylinders of the type here shown, the second stage cylinder 7 also provides an extensible tubular plunger for the first stage cylinder 6, while the third stage cylinder 8 also provides an extensible tubular plunger for the second stage cylinder 7. A piston rod 9 inside the cylinder S providestan extensible plunger for the third stage cylinder.

The outer cylinder 6 is closed at its inner end as by an end cap 10 and it is provided with a port 11, in its side near the inner end of the cylinder, through which pressure Huid may be admitted into the cylinder to effect extension of the plungers of the various stages thereof.

Each of the cylinders 6 and 7 is provided with a more or less conventional plunger sealing device 13 in its outer end portion to slidingly embrace and guide the extending and retracting movements of its plunger. The inner end of each of the second and third stage cylinders preferably has a circumferential ange 14 fixed on its exterior to slidingly engage the wall of the adjacent surrounding cylinder to thus cooperate with the sealing devices 13 in hol-ding the second and third stage cylinders in spaced concentric relation to one another and to the outer cylinder 6. These flanges have slits 15 in their peripheries to enable pressure lluid to flow therepast.

Each of the second and third stage cylinders 7 and 3 also has a ring 16 lixed to its exterior a short distance outwardly of the ange 14 thereon, and these rings cooperate with the stops 17 fixed in the outer end portions of each of the trst and second stage cylinders 6 and 7 to limit the extending motion of the plungers 7 and 8 of these cylinders. The retracting motion of the plungers 7 and 3, of course, may be limited by the engagement of Itheir inner ends with the end cap 10 `on the outer cylinder.

A split ring 21 snapped into a circumferential groove Vin the inner end portion of the second stage cylinder 7 engages the rear of the guide ange 14 on the third stage cylinder E to provide a motion transmitting connection between these cylinders so that the two move outwardly in unison Whenever pressure iluid is admitted into the inlet port 11 in the outer cylinder 6.

The third stage cylinder 8 has an end member 23 iixed p thereto and extending across its inner end, with apertures 24 in the central portion of the end member providing for the passage of pressure iluid from the inner end of the outer cylinder 6 into the inner end of the third stage cylinder 8.

One of the most important features of this invention resides in the fact thaty the plunger 9 of thethird stage cylinder 8 is provided by a tubular piston rod litting inside the third stage cylinder in spaced concentric relation thereto and having an enlarged piston 26 lixed to its innerV end. In this case, the piston and its rod 9 are guided for extending and retracting movement inside the cylinder S by means of a sealing device 27 on the periphery of the piston and a second sealing device 28 xed in the outer end portion of the third stage cylinder 8. The outwardly facing shoulder 29 at the junction between the piston 26 and its rod 9 is adapted to engage a stop 30 secured in the outer end portion of the third stage cylinder 8 to define the extended limit of the piston rod 9.

When fluid under pressure is admitted into the port 11 in the inner end portion of the outer cylinder 6, with the unit in its fully retracted position seen in Figure 1, the second and third stage cylinders are moved bodily outwardly in unison until the cylinder 7 reaches its extended limit. The third cylinder 8 is then extended from the cylinder 7 until it also reaches its outward limit of travel, at which time pressure fluid enters its inner end to act upon the piston 26 and thus effect extension of the piston rod 9 to its outer limit of travel as shown in Figure 2.

According to this invention, the third or iinal stage cylinder 8 operates as a double acting cylinder, that is, it is both extended and retracted by uid pressure. As already brought out, the piston rod 9 ofthe third stage cylinder' is extended by uid pressure acting upon the inner face of its piston 26. Retraction of the piston rod 9, however, is effected by fluid pressure admitted into the hollow interior of the piston rod 9 through a passage 32 in a head piece 33 closing the outer end of the piston rod. The inner portion of the passage 32 opens into the `interior of the hollow piston rod, 'and an angle branch 34 of the passage has its mouth opening to the exterior y of the head piece 33 to provide a down port for the third stage cylinder.

The hollow interior of the piston rod 9 is communicated with the space between the piston rod and the third stage cylinder 8 in which it operates through an angle passage in the piston having one branch 36 opening into the interior of the piston rod and its other branch 37 opening into the interior of the second stage cylinder 8. The angle passage in the piston, of course, provides for the exhaust of pressure fluid from the space between the third stage cylinder and its piston rod during extension Vof the latter, as well as for the admission of pressure tiuid into this space during retraction of the piston rod under the inuence of pressure uid admitted into the down port 34.

In order to obviate the need for exhausting pressure tiuid through the relief valve of a four-way control valve (not shown) for the unit after the plunger of the third stage cylinder has reached its retracted position, this invention provides a novel check valve mechanism 39 which is incorporated in the piston 26 of the third stage cylinder. The purpose of this check valve mechanism is to cause pressure uid admitted into the down port 34 to exhaust through the inlet port 11 in the rst stage cylinder after the piston rod 9 is fully retracted in the third stage cylinder and to thus convert the unit from double acting operation at the start of retraction to single acting operation following retraction of the piston rod 9.

The check valve mechanism is received in a single co axial bore 4t) through the piston 26. The outer end of the bore opens into the hollow interior of the piston rod, and the other end of the bore opens to the inner face of the piston and to the space in the inner end of the third stage cylinder 8 through a counterbore 41 of a diameter great enough to encompass the apertures 24 in the end member 23 on the third stage cylinder.

The check valve mechanism per se comprises inner and outer check valves 42 and 43 siidably received in the bore 40 and engageable with axially spaced `opposing valve 75 seats 44 in the bore to close the same. A compression spring 45 confined between the two check valves yieldingly holds them on their seats but permits one or the other to be moved ofi its seat in response to fluid pressure acting upon one face or the other of piston 26.

During extension of the piston rod 9 for the third stage cylinder, therefore, iiuid pressure applied to the inner face of the piston 26 acts to unseat the adjacent check valve 42 against the bias thereon, and maintains the other check valve 43 tightly engaged with its seat thus closing the bore 40 in the piston. Upon retraction of the piston rod 9, the fluid pressure manifested in its interior acts upon the check valve 43 to unseat the same against the bias exerted thereon, and maintains the other check valve 42 tightly engaged with its seat to close the bore (see Figure 3). Hence, it will be seen that the bore 40 is closed by one or the other of the check valves both during extension and retraction of the piston rod 9.

Just before the piston 26 reaches its fully retracted position, however, a pilot-like inward coaxial extension 46 on the check valve 42 strikes the end member 23 on the third stage cylinder to cause unseating of check valve 42 so that pressure uid admitted into the hollow interior of the piston rod may ow through the bore 40 and the apertures 24 in the end member 23 into the inner end of the outer cylinder 6 from whence it is exhausted through the inlet port 11. Thereafter, the cylinders 7 and 8 are retracted solely as a consequence of the load connected to the unit, with pressure fluid therein exhausting through the inlet port 11.

Still another feature of the multistage cylinder of this invention resides in the simple and low cost bleeder means incorporated therein for exhausting air from the system when the unit is filled with hydraulic liquid. For this purpose, a bleeder pipe 48 is installed in the interior of the hollow piston rod 9. One end of the pipe is anchored in the piston 26 and opens into the counterbore 41, while the outer end of the pipe is anchored in the head piece 33. The outer end of the bleeder pipe opens into an angle passage 49 in the head piece leading to the exterior thereof, the mouth of the passage being ordinarily closed by a bleeder screw 50.

When the unit is originally filled with hydraulic liquid and all of its stages are extended their full limits, the needle point on the bleeder screw 50 is backed off its seat in the passage 49 to enable air to be expelled therefrom, and it is reseated after oil only issues from the bleeder port.

In use, of course, the outer cylinder 6 is either stationarily or pivotally mounted on suitable supports (not shown). In this case, diametrically opposite trunnions 52 are fixed on the exterior of the cylinder to mount the unit for oscillatory motion about an axis normal to the axis of the cylinder. The head piece 33 may also be provided with a hushed aperture 53 to enable the piston rod 9 for the third stage cylinder to be connected to the load or mechanism to be operated.

An example .of one installation in which the multistage cylinder of this invention is especially useful is in heavy duty dump trucks wherein the dump body is pivotally supported at one end and must be swung upwardly past vertical to discharge its contents at a position at which the weight of the body no longer resists extension ofthe cylinder but instead acts to further extend the cylinder. In that case, the dump body is swung backwardly toward and slightly beyond the vertical during the power return stroke of the piston rod 9 for the third stage cylinder.

From the foregoing description, taken together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides a simple, low cost, but reliable expedient for effecting double acting operation of the nal stage cylinder of a multistage or telescoping hydraulic cylinder.

What I claim as my invention is:

l, A uid pressure operated device of the type wherein il L J pressure fluid entering a cylinder through an inlet in its inner end acts upon the adjacent face of a piston in the cylinder to propel the piston toward the outer end of the cylinder and thus eiects extension of a piston rod secured to the piston and projecting from the outer end of the cylinder, and wherein pressure fluid admitted into the space between the cylinder and piston rod acts upon the other face of the piston and propels the same toward the inner end of the cylinder to thus effect retraction of the piston rod, characterized by: the fact that said piston rod is tubular and has its hollow interior communicated with the space between the cylinder and the piston rod at a location adjacent to said piston; by the provision of a head piece closing the outer end of the piston rod and having a passage therein through which pressure uid may be admitted into the hollow interior of the piston rod; by the fact that the piston has an axial bore therethrough to communicate the hollow interior of the piston rod with the inner end of the cylinder; by the provision of axially spaced opposing valve seats in said bore; by the provision of check valve means in said bore cooperable with said valve seats, said check valve means being adapted to engage the outer valve seat and thus close said bore in response to the ow of pressure fluid into the inner end of the cylinder, and being adapted to engage the inner valve seat and thus close said bore in response to the admission of pressure fluid into the hollow interior of the piston rod; and by the provision of interengaging means on the inner end of the cylinder and said check c, valve means defining cooperatlng abutments engageable upon final retracting movement of the piston under the inuence of pressure fluid admitted into the hollow interior of the piston rod to effect unseating of said check valve means from the inner valve seat and consequently opening of the bore in the piston for the flow of pressure fluid therethrough to the inlet in the inner end of the cylinder.

2. In a iluid pressure operated device of the character described: a cylinder having an end member xed to one end thereof and extending thereacross, said end member having an aperture through which pressure uid may enter the cylinder; a tubular piston rod in the cylinder in spaced concentric relation thereto and projecting from the other end of the cylinder; a piston xed to the inner end of the piston rod and slidable outwardly of the cylinder in consequence of the admission of pressure fluid into the inner end of the cylinder, said piston havingr an axial bore therethrough to communicate the hollow interior of the piston rod with the inner end of the cylinder,

and the interior of the piston rod being communicated with the space between the cylinder and piston rod at a location adjacent to said piston; a head piece closing the outer end of the piston rod and having a passage therein through which pressure iiuid may be admitted into the hollow interior of the piston rod and to the space between it and the cylinder to propel the piston inwardly of the cylinder; means in the piston bore defining a pair of axially spaced opposing valve seats; a pair of check valves in said bore each yieldingly biased into engagement with one of said valve seats to close the bore but movable off its seat by fluid pressure acting upon the adjacent end of the piston; and cooperating abutments on the end member of the cylinder and on the adjacent check valve engageable upon :etraction of the piston to a position contiguous to the end member to effect unseating of said adjacent check valve.

3. The fluid pressure operated device set forth in claim 2 further characterized by: the provision of a bleeder pipe extending lengthwise through the hollow interior ol' the piston rod between the piston and said head piece with its ends anchored therein, the inner end of said pipe communicating with the inner end of the cylinder and the outer end of said pipe opening to a passage in the head piece leading to the exterior thereof; and a bleeder screw closing the ymouth of said passage in the head piece. v

4. The fluid pressure operated device set forth in claim 2 further characterized by the fact that said head piece has a hole therethrough outwardly of the passage therein to provide for connection of the piston rod with a load.

5. In a fluid pressure operated device of the character described: a tubular cylinder having an end member fixed to one end thereof and extending thereacross, said end member having an aperture through which pressure fluid may enter the cylinder; la piston in the cylinder movable outwardly of the cylinder from a retracted position therein engaging said end member in consequence of the admission of pressure fluid into the inner end of the cylinder, said piston having a passage therein one end portion of which opens to the inner face of the piston and the other end portion of which opens to the outer face of the piston; a tubular piston rod fixed to the piston and extending outwardly therefrom in spaced concentric relation to the cylinder, the outer end of said piston rod occupying a position close to the outer end of the cylinder when the piston is in said retracted position thereof, and the inner end portion of the piston rod encircling and having its interior communicating with the outer portion of said passage in the piston `and also communieating with the space between the piston rod and the cylinder; a head piece closing the outer end of the piston rod and projecting outwardly from the cylinder, said head piece having a passage therein leading from the interior of the piston rod to the exterior of the head piece at a zone thereof spaced outwardly of the outer end of the cylinder when the piston is in said retracted position thereof, said head-piece passage providing for the admission of pressure uid into the interior of the piston rod and to the space between the rod and the cylinder necessary to effect retraction of the piston and its rod; means in the inner and outer portions of said piston passage defining a pair of opposing valve seats; a pair of check valves in said passage each yieldingly biased into engagement with one of said valve seats to close the passage but movable off its seat by iluid pressure acting upon the adjacent end of the piston; and cooperating abutments on the end member of the cylinder` and the adjacent check valve engageable upon retraction of the piston to a position contiguous to the end member to effect unseating of said adjacent check valve.

6. In a telescoping hydraulic cylinder, the combination of: a stationary single acting outer cylinder, and an outwardly extensible double acting tubular inner cylinder therein, the outer cylinder having an end cap at its inner end and having a port through which pressure iluid may be admitted into the inner end portion of Isaid outer cylinder; said inner cylinder having an apertured end member fixed to and extending across its inner'end and against which pressure fluid introduced into the inner end portion of the outer cylinder may act to impart outward extending movement to said inner cylinder; outwardly extensible means in said inner cylinder comprising a hollow elongated piston rod having a piston on its inner end slidably fitting in the inner cylinder and engageable with the end member thereof to define the retracted position of the piston and its rod, said piston rod being extensible outwardly from the inner cylinder as a consequence of the ilow of pressure fluid into the inner end of the inner cylinder; passage means in said extensible means adjacent to the inner end of the piston rod for communicating the hollow interior of the latter with the space between the piston rod and the inner cylinder; a head piece closing the outer end of the piston rod and having a passage therein through which pressure duid may be admitted into the hollow interior of the piston rod and to said space between the rod and the inner cylinder to propel the piston and its rod inwardly of the inner cylinder; means defining a passage in the piston for communicating the hollow interior of the piston rod with the inner ends of the inner and outer cylinder; a check yalve in each end portion of said passage yieldingly biased toma position closing the passage,the inner check valve being adapted to open in response to the ilow of pressure uid into the inner end of the inner cylinder, and the outer check valve being adapted to open in response to the flow of pressure uid into the outer end of the hollow piston rod; and cooperating abutments on the end member of the inner cylinder and on the adjacent check valve engageable upon retract-ion of the piston to a position contiguous to said 1() end member to elfect nnseating of the adjacent check valve.r n 4 7. The telescoping hydraulic cylinder set vfortli in clairn 6 wherein said check valves operate in a common bore extendingraxially through the piston to define said passage therein, and wherein said valves are held yieldingly en,- gaged with opposing valve seats in the bore by a single compression spring confined between the check valves.

No references cited 

